52 PAPERS ON ZOOLOGY OF MICHIGAN 



tail Bay. They were found among the submerged vegetation in fairly 

 deep water. No adults were secured. The eggs of this species, which 

 are laid in strings, were found attached to aquatic vegetation both in 

 North Fishtail Bay and at the mouth of Bessey Creek. 



GENUS CORD U LI A LEACH. 



Cordulia shurtleffi Scudder. — Nymphs of this species were taken in 

 Bessey Creek although they appear to be rather uncommon, judging 

 from the number appearing in the collections. These nymphs were 

 found along the shore in debris of various sorts. 



Subfamily Libellulinae. 



KEY TO THE GENERA OF LIBELLULINAE. 



Imagos. 



A. Triangle oi the fore mng not placed distinctly beyond the level of the apex of the triangle 

 of the hind wing; ends of pterostigma not distinctly divergent. 



B . Sectors of the arculus, veins Mi to 3 and Mi, in the fore wing more oc less com- 

 pletely fused for a short distance beyond the arculus; triangle of the fore wing 

 not greatly produced posteriorly, normally containing bur a single cross-vein. 

 C . Vein Cui of the hind wing departing from the triangle at the hind angle. 

 D. Sectors of the arculus contiguous but incompletely fused for 

 a distance beyond the. arculus; wings generally spotted with 

 yellow or reddish brown. 



Celithemis 



DD. Sectors of the hind wing distinctly fused for a distance beyond 

 the arculus. 



Sympetrum 



CC. Vein Cui of the hind wing migrating a litile way up the outer side of 

 the triangle. 



Pachydiplax 



BB . Sectors of the arculus of the fore wing contiguous but not completely fused be- 

 yond the point of their departure from the arculus. 



Libellula 



AA. Triangle of the fore wing placed distinctly beyond the level of the apex of the triangle of 

 the hind wing. 



Tramea 



Nymphs. 



A. Basal segment of the nind tarsus more than hail as long as the second segment. 

 B . No dorsal hooks. 



Pachydiplax 



BB . With dorsal hooks at least on the middle abdominal segments. 

 C. Abdomen ovate. 



D. Lateral spines long and straight. 



Celithemis 



DD. Lateral spines short and more or less incurved. 



Sympetrum 



CC. Abdomen lancolate; five to ten lateral setae. 



Libellula 



AA. Basal segment of the hind tarsus only hair as long as the second segment; lateral setae 

 ten or more. 



Tramea 



